An optical recording medium, such as a CD-R/RW, a DVD-R/RW/RAM and a Blue-Ray disk, and a display device, such as a liquid crystal display and an organic luminescent display have at least one layer of a reflection film formed therein. For instance, FIG. 1 shows a structure of an HD-DVD (one-sided, dual-layer rewritable disk) which has been developed in recent years, as an example of the optical recording medium. As shown in the example, the optical recording medium has a multilayer structure comprising the reflection film in addition to a recording layer which plays a predominant role of the function of the optical recording medium, a protective layer and a thermal diffusion layer.
Many conventional reflection films are made from silver. This is because silver has a high reflectance and is more inexpensive than gold having the high reflectance similarly to silver. Silver also has excellent optical transparency when the film thickness is appropriately adjusted, accordingly can be possibly used as a semi-transparent reflection film, and from this fact, has been applied to an optical recording medium being developed now (cf. FIG. 1).
On the other hand, silver has a problem of changing the color to black through being corroded to decrease its reflectance, because of being inferior in corrosion resistance. The factor of causing corrosion in a reflection film is, for instance, an organic dye applied in a recording layer of an optical recording medium, though it varies depending on an applied medium and device. Then, the reflection film shows lower reflectance after having been corroded by the organic dye for a long period of use. In addition, the reflection film in a display device may cause corrosion due to the atmospheric moisture. For this reason, a thin film made from a silver alloy has been developed which contains various elements in a silver matrix, so as to solve the problem of the corrosion resistance of silver.
For instance, Patent Document 1 discloses a silver alloy containing 0.5 to 10 atom % ruthenium and 0.1 to 10 atom % aluminum, and Patent Document 2 discloses a silver alloy containing 0.5 to 4.9 atom % palladium. In addition, Patent Document 3 and Patent Document 4 disclose a silver alloy containing Ca, V and Nb, and the like.
Patent Document 1: Japanese Patent Application Laid-Open No. 134715/1999
Patent Document 2: Japanese Patent Application Laid-Open No. 2000-109943
Patent Document 3: Japanese Patent Application Laid-Open No. 243509/1994
Patent Document 4: Japanese Patent Application Laid-Open No. 2003-6926